<!doctype html>
<meta charset="utf-8">
<title>getCaretPositionFromPoint should return the correct offset even in iframes with transformation</title>
<link rel="help" href="https://drafts.csswg.org/cssom-view-1/#dom-document-caretpositionfrompoint">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1546612">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  #actual {
    transform: translateX(100px);
  }
</style>
<iframe id="expected"></iframe>
<br>
<iframe id="actual"></iframe>
<script>
  const expectedFrame = document.getElementById("expected");
  const actualFrame = document.getElementById("actual");

  const getCaretPositionOffset = frame => {
    const source = `<!doctype html><meta charset="utf-8"><h1>title</h1><p>paragraph</p>`

    const elementCenter = elem => {
      const rect = elem.getBoundingClientRect();
      return [rect.x + rect.width / 2, rect.y + rect.height / 2];
    };

    return new Promise((resolve, reject) => {
      frame.srcdoc = source;
      frame.onload = () => {
        try {
          const frameDoc = frame.contentDocument;
          const {offset} = frameDoc.caretPositionFromPoint(
            ...elementCenter(frameDoc.querySelector("h1"))
          );
          resolve(offset);
        } catch (error) {
          reject(error);
        }
      };
    });
  };

  promise_test(async () => {
    assert_equals(...await Promise.all([
      getCaretPositionOffset(expectedFrame),
      getCaretPositionOffset(actualFrame)
    ]), "caret offset");
  }, "iframe's with equal content should report the same caret offset");
</script>
